1. Field of the Invention
The present invention is related to a method of redundancy of a network, especially to a method of redundancy of a ring network with broadcast storm prevention mechanism.
2. Description of Related Art
With the rapid growth of the modern technology, various communication devices and computer networks make information spread much more rapidly. For companies, businesses, and even the common people, keeping the information flowing without obstruction is very important. Generally, communication networks can be defined briefly as the whole operation environment with communication devices connecting to one another. According to the scope of the region being covered, communication networks can be classified into three primary types, including local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN). Among the three types of communication networks, the LAN is the networks with the smallest scope of region covered, usually used in the same office, building, or campus.
In the world of communication networks, every node in the networks must obey the same rule for the exchange of information to be established successfully. Therefore, communication protocols are formed with specific requirements and format. The most common communication protocols are the Open System Interconnection model (OSI model) set up by the International Organization for Standardization (ISO), and the series of IEEE 802 set up by the Institution of Electrical and Electronics Engineers (IEEE). Therein, Ethernet is used as one of the common schemes of LAN.
A network structure is not only about the topology of network connection, but also about the physical communication media and the access of information. OSI model acts as the reference concept for the network structure, as it doesn't address any specific implementation. However, the Ethernet, Token Ring network, Attached Resource Computer network (ARCnet), Fiber Distributed Data Interface (FDDI), and the AppleTalk, etc., are some of the communication protocols of network structure that may be attached to the OSI model.
Generally speaking, every node of the networks applied in the LAN and industrial automatic system has a network switch, which is used to connect related devices with the networks, these related devices may includes a computer, communication devices, and terminals, so as to facilitate information exchanging.
The topology of networks includes various kinds, such as line, ring, bus, star, mesh, and tree, etc., wherein the ring network connects the nodes of the network serially, additionally with the first node and the last node being connected to each other, thereby forming a close ring network. The nodes of the ring network can communicate to one another through the transmission lines of the ring network. However, if the information communicating on the ring network keeps looping without a stopping mechanism, the bandwidth of the ring network will be occupied, and thus new information will not be allowed to transmit; this problem is referred to as the broadcast storm. To overcome the problem, a blocked port is set in the ring network for stopping the information from passing through. Therefore, information will not be transmitted endlessly.
Moreover, because of the characteristic of communication within the ring network, when a node or a transmission line of the ring network is broken, the other nodes of the ring network will be influenced (since it is a circular closed loop) and cause the ring network to break down. Therefore, ensuring the communication flowing without obstruction is very important. The applying of redundancy scheme for improving the stability of the ring network is the algorithm of Rapid Spanning Tree protocol (RSTP). In RSTP, when a port that is being blocked so as to prevent endless loop of information (to be referred to as blocked port) detects any of the node or transmission line of the ring network failing, the blocked port changes its state into forward so as to keep the over-all network communicable, thereby fulfilling its purpose of redundancy. And after the failed node or transmission line is repaired, the state of the blocked port then recovers back to the initial status of being blocked.
However, due to the protocol convergence algorithm, the state changing of the blocked port is not fast enough in RSTP algorithm. Thus, the packets transmitted through the transmission line may be lost during the state changing, causing the system to fail due to needed information being lost.